1. Field of the Invention
The invention relates to a fuel supply system for an internal combustion engine provided with a fuel injection mechanism that injects fuel at high pressure into a cylinder (i.e.; a fuel injector for in-cylinder injection, hereinafter referred to as “in-cylinder fuel injector”) and a fuel injection mechanism that injects fuel into an intake passage or an intake port (i.e., a fuel injector for intake passage injection, hereinafter referred to as “intake passage fuel injector”). More particularly, the invention relates to a fuel supply system that can improve startability of an internal combustion engine.
2. Description of the Related Art
A gasoline engine is known which is provided with a fast fuel injection valve for injecting fuel into a combustion chamber of the engine (i.e., an in-cylinder fuel injector) and a second fuel injection valve for injecting fuel into an intake passage (i.e., an intake passage fuel injector), and divides the injected fuel between the in-cylinder fuel injector and the intake passage fuel injector according to the engine speed and engine load. Also, a direct injection gasoline engine is also known which is provided with only a fuel injection valve for injecting fuel into the combustion chamber of the engine (i.e., an in-cylinder fuel injector). In a high pressure fuel system that includes an in-cylinder fuel injector, fuel of which the pressure has been increased by a high pressure fuel pump is supplied to the in-cylinder fuel injector via a delivery pipe. The in-cylinder fuel injector then injects the high pressure fuel into the combustion chamber of each cylinder of the internal combustion engine.
In addition, a diesel engine is also known which has a common rail type fuel injection system. In this common rail type fuel injection system, fuel which has been increased in pressure by a high pressure fuel pump is stored in a common rail. The high pressure fuel is then injected into the combustion chamber of each cylinder of the diesel engine from the common rail by opening and closing an electromagnetic valve.
In order to increase the pressure of (i.e., pressurize) the fuel in this kind of internal combustion engine, a high pressure fuel pump is provided which is driven by a cam provided on a driveshaft that is connected to a crankshaft of the internal combustion engine.
Japanese Patent Application Publication No. JP-A-2005-139923 describes a high pressure fuel supply system for an internal combustion engine that can reduce vibrational noise when only a small amount of fuel is required by the internal combustion engine, such as during idling, while being able to deliver the necessary amount of fuel over the entire operating range of the internal combustion engine. This high pressure fuel supply system for an internal combustion engine has a two single plunger type high pressure fuel pumps each of which have a spill valve that spills fuel drawn into a pressurizing chamber that is divided by a cylinder and a plunger that moves back and forth in the cylinder, from that pressurizing chamber. When fuel is pressurized and delivered from the pressurizing chamber to the high pressure fuel system, the amount of fuel delivered is adjusted by controlling the spill valve open and closed. One of these high pressure fuel pumps is a first high pressure fuel pump in which the lift amount of the plunger is small and the other high pressure fuel pump is a second high pressure fuel pump in which the lift amount of the plunger is large. In addition to these two high pressure fuel pumps, the high pressure fuel supply system for an internal combustion engine also includes control means. The control means controls the spill valve of each high pressure fuel pump according to the amount of fuel required by the internal combustion engine, such that fuel is pressurized and delivered using only the first high pressure fuel pump when the amount of required fuel is small, and fuel is pressurized and delivered using at least the second high pressure fuel pump when the amount of required fuel is large.
According to this high pressure fuel supply system for an internal combustion engine, of the two high pressure fuel pumps, the first high pressure fuel pump has a plunger with a small lift amount so the rate of pressure increase is small and a large amount of water hammer is also self-suppressed. That is, with the high pressure fuel supply system, the vibrational noise produced when the required fuel quantity is small can be preferably reduced by controlling the spill valve of each of the high pressure fuel pumps so that only the first high pressure fuel pump is used when the amount of fuel required for the internal combustion engine is small such as during idling. On the other hand, the second high pressure fuel pump has a plunger with a large lift amount so pressurizing and delivering fuel using at least this second high pressure fuel pump also makes it possible to deliver the required fuel quantity when the amount of fuel required by the internal combustion engine increases to the point where it can no longer be delivered by the first high pressure fuel pump alone. That is, providing two high pressure fuel pumps having plungers with different lift amounts in this way enables the required amount of fuel to be delivered throughout the entire operating range of the internal combustion engine, while reducing vibrational noise when the amount of required fuel is small.
In Japanese Patent Application Publication No. JP-A-2005-139923, the high pressure fuel supply system for a V-type 8 cylinder internal combustion engine having an in-cylinder fuel injector in each cylinder is provided with a high pressure fuel pump for each bank. Tip ends that branch off from a low pressure fuel passage which is connected to the fuel tank are connected to galleries of these high pressure fuel pumps. For each bank, a pulsation damper is provided midway between the branch portion of the low pressure fuel passage and the portion that connects with the gallery. This pulsation damper suppresses the pulsation in the fuel pressure in the low pressure fuel passage when the high pressure fuel pump is operating. At engine startup in this kind of a direct injection engine having only an in-cylinder fuel injector, fuel is unable to be delivered by the high pressure fuel pump until the engine turns over. Therefore, low pressure fuel is delivered by a feed pump to the fuel injection for in-cylinder injection. Therefore, the pulsation damper is designed to provide communication between the high pressure pipe system and the low pressure pipe system. For example, FIG. 6 is a sectional view of such a pulsation damper 221, FIG. 7 is a sectional view taken along line VII-VII of FIG. 6, and FIG. 8 is a sectional view taken along line VIII-VIII of FIG. 7. As shown in FIGS. 6 to 8, grooves 223A, 223B, 223C, and 223D are provided in an end face (i.e., the upper surface in FIG. 8) that abuts against a contacting member 226A of the pulsation damper 221. Therefore, when the feed pressure is low, the spring 226D presses the contacting member 226A against the upper surface of the member that forms the inlet 222 and the outlet 224. In this way, the structure is such that even if pressure is applied by the spring 226D, the grooves 223A, 223B, 223C, and 223D enable fuel delivered from the inlet 222 (i.e., the feed pump side) to flow into the outlet 224 (i.e., the high pressure fuel pump side) as shown by the dotted line in FIG. 8.
On the other hand, as described above, an engine is known which includes, for each cylinder, an in-cylinder fuel injector that injects fuel into a combustion chamber of the engine and an intake passage fuel injector that injects fuel into an intake passage. In this engine, fuel is injected divided between the in-cylinder fuel injector and the intake passage fuel injector according to the engine speed and the load on the internal combustion engine. This engine is also provided with the pulsation damper shown in FIGS. 6 to 8.
However, in this kind of engine, the following problems occur when starting the engine by injecting fuel with an intake passage fuel injector. When fuel is delivered by a feed pump at engine startup, the volume of pipe that needs to be charged with fuel becomes significantly larger. That is, when the engine is started with fuel injected from the intake passage fuel injector, despite the fact that fuel can be delivered to the intake passage fuel injector with the feed pump by simply charging only the low pressure pipe with fuel, the pulsation damper is structured such that the high pressure pipe system and the low pressure pipe system are communicated or open to one another. Therefore, fuel is unable to be delivered to the intake passage fuel injector by the feed pump unless both the low pressure pipe and the high pressure pipe are charged with fuel. As a result, it takes time for the feed pressure to rise, thereby adversely affecting startability (i.e., increasing the start time).